CVE-2021-21696: Jenkins core Shared Groovy Libraries Plugin Vulnerability

HIGH
Advisory Identifier: GHSA-c5r9-rx53-q3gf
Share
CVSS 8.8
CWE-693
Published
Advisory Summary

CVE-2021-21696 is a HIGH (CVSS 8.8) shared groovy libraries plugin vulnerability (CWE-693: Protection Mechanism Failure) affecting Jenkins core libraries in the Maven ecosystem. The issue involves shared groovy libraries plugin. Remediation is available by upgrading affected packages to version 2.303.3, 2.319.

CVE-2021-21696 at a Glance

CVE Identifier CVE-2021-21696
GHSA Identifier GHSA-c5r9-rx53-q3gf
Severity HIGH
CVSS v3.1 Base Score 8.8
CWE Classification CWE-693: Protection Mechanism Failure
Affected Product Jenkins core
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 8.8

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required Low (PR:L)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity High (I:H)
Availability High (A:H)

How to Fix CVE-2021-21696

To remediate this vulnerability, upgrade all affected Jenkins core dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

org.jenkins-ci.main:jenkins-core fixed: 2.303.3 
<dependency>
    <groupId>org.jenkins-ci.main</groupId>
    <artifactId>jenkins-core</artifactId>
    <version>2.303.3</version>
</dependency>
org.jenkins-ci.main:jenkins-core fixed: 2.319 
<dependency>
    <groupId>org.jenkins-ci.main</groupId>
    <artifactId>jenkins-core</artifactId>
    <version>2.319</version>
</dependency>
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

mvn dependency:tree -Dincludes=org.jenkins-ci.main

How to Check if You Are Affected

To determine whether your Java application is affected by CVE-2021-21696, inspect your build dependencies using the Maven Dependency Plugin:

mvn dependency:tree -Dincludes=org.jenkins-ci.main

Analyze the terminal output to locate any version of Jenkins core in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.303.3), your application is affected.

Note: The mvn dependency:tree -Dincludes=org.jenkins-ci.main command inspects the resolved dependency graph declared in your project's POM files; it does not perform automated security scanning or inspect runtime dynamic classpaths. Always verify runtime container classpaths and shaded JARs.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-693: Protection Mechanism Failure, where the product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product. In Jenkins core, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

Jenkins 2.318 and earlier, LTS 2.303.2 and earlier does not limit agent read/write access to the `libs/` directory inside build directories when using the `FilePath` APIs. This directory is used by the Pipeline: Shared Groovy Libraries Plugin to store copies of shared libraries. This allows attackers in control of agent processes to replace the code of a trusted library with a modified variant, resulting in unsandboxed code execution in the Jenkins controller process. Jenkins 2.319, LTS 2.303.3 prohibits agent read/write access to the `libs/` directory inside build directories. If you are unable to immediately upgrade to Jenkins 2.319, LTS 2.303.3, you can install the [Remoting Security Workaround Plugin](https://www.jenkins.io/redirect/remoting-security-workaround/). It will prevent all agent-to-controller file access using FilePath APIs. Because it is more restrictive than Jenkins 2.319, LTS 2.303.3, more plugins are incompatible with it. Make sure to read the plugin documentation before installing it. It is not easily possible to [customize the file access rules](https://www.jenkins.io/doc/book/security/controller-isolation/agent-to-controller/#file-access-rules) to prohibit access to the `libs/` directory specifically, as built-in rules (granting access to `<BUILDDIR>` contents) would take precedence over a custom rule prohibiting access.

CVE-2021-21696 Affected Jenkins core Versions

2 component(s)
Fixed Versions:
2.303.32.319
Product / Package Ecosystem Affected Versions Fixed Version
org.jenkins-ci.main:jenkins-core
maven/org.jenkins-ci.main/jenkins-core
Maven
< 2.303.3
2.303.3
org.jenkins-ci.main:jenkins-core
maven/org.jenkins-ci.main/jenkins-core
Maven
≥ 2.304
< 2.319
2.319

References

NVD — CVE-2021-21696 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-21696
Security Fix Commit FIX COMMIT
https://github.com/jenkinsci/jenkins/commit/93451e20c20cfd84badeb0f37c38d4c0c7a5dad3
Jenkins core Source Repository REPOSITORY
https://github.com/jenkinsci/jenkins
Jenkins core Security Information SECURITY
https://www.jenkins.io/security/advisory/2021-11-04/#SECURITY-2423
Jenkins core Security Information SECURITY
http://www.openwall.com/lists/oss-security/2021/11/04/3

Frequently Asked Questions

What is CVE-2021-21696?
CVE-2021-21696 is a security vulnerability in Jenkins core involving Shared Groovy Libraries Plugin under CWE-693: Protection Mechanism Failure.
Which Jenkins core versions are affected?
Affected versions include releases prior to 2.303.3, 2.319 across affected packages: org.jenkins-ci.main:jenkins-core.
What version fixes CVE-2021-21696?
Upgrading to 2.303.3, 2.319 (or the latest patched release for your respective branch) resolves the vulnerability.
Is jenkins-core affected?
Yes, org.jenkins-ci.main:jenkins-core is affected in releases prior to 2.303.3, 2.319. Upgrade your dependency to 2.303.3, 2.319 or later.
What is the CVSS score of CVE-2021-21696?
CVE-2021-21696 has a CVSS v3.1 base score of 8.8 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2021-21696?
CVE-2021-21696 is classified under CWE-693: Protection Mechanism Failure (The product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product.).
How can I check Maven dependencies for CVE-2021-21696?
Run the dependency tree command: 'mvn dependency:tree -Dincludes=org.jenkins-ci.main'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-c5r9-rx53-q3gf",
  "modified" : "2022-12-16T20:43:58Z",
  "published" : "2022-05-24T19:19:43Z",
  "aliases" : [ "CVE-2021-21696" ],
  "summary" : "Agent-to-controller access control allowed writing to sensitive directory used by Jenkins Pipeline: Shared Groovy Libraries Plugin",
  "details" : "Jenkins 2.318 and earlier, LTS 2.303.2 and earlier does not limit agent read/write access to the `libs/` directory inside build directories when using the `FilePath` APIs. This directory is used by the Pipeline: Shared Groovy Libraries Plugin to store copies of shared libraries.\n\nThis allows attackers in control of agent processes to replace the code of a trusted library with a modified variant, resulting in unsandboxed code execution in the Jenkins controller process.\n\nJenkins 2.319, LTS 2.303.3 prohibits agent read/write access to the `libs/` directory inside build directories.\n\nIf you are unable to immediately upgrade to Jenkins 2.319, LTS 2.303.3, you can install the [Remoting Security Workaround Plugin](https://www.jenkins.io/redirect/remoting-security-workaround/). It will prevent all agent-to-controller file access using FilePath APIs. Because it is more restrictive than Jenkins 2.319, LTS 2.303.3, more plugins are incompatible with it. Make sure to read the plugin documentation before installing it.\n\nIt is not easily possible to [customize the file access rules](https://www.jenkins.io/doc/book/security/controller-isolation/agent-to-controller/#file-access-rules) to prohibit access to the `libs/` directory specifically, as built-in rules (granting access to `<BUILDDIR>` contents) would take precedence over a custom rule prohibiting access.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.jenkins-ci.main:jenkins-core"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.303.3"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.303.2"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "org.jenkins-ci.main:jenkins-core"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.304"
      }, {
        "fixed" : "2.319"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.318"
    }
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-21696"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/jenkinsci/jenkins/commit/93451e20c20cfd84badeb0f37c38d4c0c7a5dad3"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/jenkinsci/jenkins"
  }, {
    "type" : "WEB",
    "url" : "https://www.jenkins.io/security/advisory/2021-11-04/#SECURITY-2423"
  }, {
    "type" : "WEB",
    "url" : "http://www.openwall.com/lists/oss-security/2021/11/04/3"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-693" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2022-06-23T06:47:00Z",
    "nvd_published_at" : "2021-11-04T17:15:00Z"
  }
}